Barrier coatings which prevent, reduce, or inhibit the permeation of a selected substrate with a gas, vapor, chemical and/or aroma have been widely described, and such coatings are used in a variety of industries, e.g., the packaging industry, automobile industry, paint industry, and tire industry. For example, butyl rubber in automobile tires has been coated with formulations which includes a polymer and a platelet filler, in order to reduce the air permeability of the tire. See, e.g., U.S. Pat. Nos. 4,911,218 and 5,049,609. Tires with integral innerliners are disclosed in U.S. Pat. No. 5,178,702, wherein the tire includes rubber laminate in which at least two layers are barrier layers having 100 parts by weight rubber, 100 parts by weight acrylonitrile/diene polymer and about 25-150 parts by weight of platelet filler of unspecified width and thickness. These compositions are stated to reduce the costs of the innerliners while maintaining flexibility and barrier performance.
The use of exfoliated silicates to produce nanocomposite barrier coatings has been achieved by several methods. The most widely used has been by combining a dissolved polymer with exfoliated filler. Water soluble polymers such as polyvinyl alcohol (PVOH) have been combined with water exfoliated filler such as vermiculite. See, Japanese Patent 11-246729, Sep. 14, 1999, “Gas-Barrier Poly(vinyl alcohol)/poly (acrylic acid) Compositions and their Laminates and Shaped Articles.” Sumitomo Chemical Co., Ltd. Polycarbonate polymers have been dissolved in toluene and combined with organically functionalized filler to form good barrier coatings. W. J. Ward et al., “Gas Barrier Improvement Using Vermiculite and Mica in Polymer Films”, Journal of Membrane Science, 55:173-180 (1991). Other polymers have also been made into improved barrier coatings by dissolving them in a solvent, and using an organically functionalized filler to improve the barrier properties. See, e.g., Yano et al., “Synthesis and Properties of Polyimide-Filler Hybrid Composites”, Journal of Polymer Science A: Polymer Chemistry, 35, 2289 (1997).
There are several examples of using an aqueous dispersion of exfoliated filler with an aqueous dispersion of polymer to form a nanocomposite. Most of that work used elastomeric polymers in suspension. See, for example, Wu, Y-P et al., “Structure of Carboxylated Acrylonitrile-Butadiene Rubber (CNBR)-Filler Nanocomposites by Co-coagulating Rubber Latex and Filler Aqueous Suspension”, Journal of Applied Polymer Science, 82, 2842-2848 (2001); Wu, Y-P et al., “Structure and Properties of Nitrile Rubber (NBR)-Filler Nanocomposites by Co-coagulating NBR Latex and Filler Aqueous Suspension”, Journal of Applied Polymer Science, 89, 3855-3858 (2003); Varghese and Karger-Kocsis, “Natural Rubber-Based Nanocomposites by Latex Compounding with Layered Silicates”, Polymer (in press) (2003); Feeney et al., U.S. Pat. No. 6,087,016, “Barrier Coating of an Elastomer and a Dispersed Layered Filler in a Liquid Carrier”, Jul. 11, 2000; Feeney et al., U.S. Pat. No. 6,232,389, “Barrier Coating of an Elastomer and a Dispersed Layered Filler in a Liquid Carrier and Coated Articles”, May 15, 2001; Goldberg et al., “Nanocomposite Barrier Coatings for Elastomeric Applications”, Materials Research Society, Symposium T: Polymer nanocomposites, paper T4.7, (April 2002); and Goldberg et al., “Elastomeric Barrier Coatings for Sporting Goods”, ACS Rubber Section, Apr. 29, 2002, paper 17, published in Rubber World, vol. 226, No. 5, p. 15 (August 2002).
There are also examples of pigment containing coating compositions for controlling coating thickness and uniformity. For instance, U.S. Pat. No. 4,171,228 to Lowrey discloses a pigment composition for high build protective coating, which comprises a combination of low density pigments of smooth nodular shape having a particle size of 325 microns with not less than 40 percent by weight retained on a 325 mesh screen and a second pigment having a median particle diameter ranging from 0.5 to 20 microns. The coating material formed therefrom has a minimum dry film thickness of approximately 100 microns per coat.
U.S. Pat. Nos. 6,261,631 and 6,488,719 to Lomasney et al. describe a method for controlling wet film thickness of clear coatings by means of color-dissipating dye. However, the dye as used therein dissipates color ranging from a few hours to a few days, thus may not be suitable for coatings wherein there is a need for clear transparent coating having no color.
U.S. Pat. No. 6,410,926 to Munro et al. discloses a coating with optical taggent, which is used for determining the thickness of a dryable or curable film-forming coating by incorporating a fluorescent component into the coating. The fluorescent component is either a resin solid of the coating, a fluorescent dye or a fluorescent dye attached to a resin solid of the coating. The coating is exposed to ultraviolet or visible light which causes the fluorescent component to fluoresce. The intensity of the fluorescence of the coating is measured and the thickness or weight of the coating is determined from a known mathematical relationship between the fluorescence intensity of the coating when exposed to the light and the thickness or weight of the coating. However, such fluorescent components are generally not suitable for applications in water dispersible coating compositions.
Other references of interest include U.S. Pat. No. 4,472,538 to Kamigaito et al.; U.S. Pat. No. 4,889,885 to Usuki et al.; U.S. Pat. No. 6,087,016 to Feeney et al.; and U.S. Pat. No. 6,232,289 to Feeney et al.
Despite advances in the art, there exists a need for an aqueous coating composition containing a dye for improved quality control and so forth in connection with transparent thin barrier films. Such a coating would be particularly useful in packaging applications among others where the coating thickness of the coated packaging can be measured rapidly and the coating thickness is preferably uniform. There further exists a need for a transparent coating material containing an invisible marker dye that imparts no observable color or appearance change, and thus can also function as a marker to determine if a particular product has used a particular aqueous barrier coating composition.